Other versions exist on this site from various publications. This one is from the Radio Electronics Experimenter from 1990. The bargraph circuit uses the UAA170.
This circuit was originally created to monitor signals from a remote-control transmitter for the...
In this circuit the CA3140, an operational amplifier, is used as a comparator with the zener diode...
This circuit was found in old documentation. The frequency depends on R1 and C1. For the...